1. Field of the Invention
The present invention generally relates to air filtration systems and, more particularly, to tunable air filtration systems for combustion engines, such as vehicle engines.
2. Description of the Background
Internal combustion engines operate on well known principles. A piston compresses an air-fuel mixture in a cylinder. The mixture is ignited to rapidly increase the temperature and pressure in the cylinder which displaces the piston thereby converting the chemical energy of the fuel into kinetic mechanical energy capable of doing work. The power output of the engine, i.e. the rate at which work is performed or energy is converted, is a function of many variables, including in particular, the relative and absolute component quantities of the fuel-air mixture in the cylinder.
In multi-cylinder engines, fuel is typically delivered to the cylinders from the fuel tank by individual carburetors or pressurized fuel injectors. Outside air is drawn in and delivered to the carburetors through an air intake system. Older engines draw air directly from the surroundings into each individual carburetor. However, most modern engines instead draw air into a plenum or “air box” which is connected by individual hoses to each carburetor, or directly to the intake ports in fuel-injected engines. This allows the use of a single air filter provided between the outside air and inside of the plenum or air box to remove particulate matter that may damage the engine. Designers design carefully-calibrated air boxes and manifolds to ensure the free flow of air to the engine under all operating conditions, so as not to negatively impact engine performance if proper quantities of air cannot be delivered to each cylinder. This applies to 99% of all motorcycles.
Vintage Modern motorcycle air boxes and certain modern motorcycle air boxes are large and unsightly, difficult to remove and reinstall as is necessary in order to perform certain maintenance on the carburetors and the engine, and are expensive to replace. Consequently, it is not uncommon for operators to remove the air box altogether so as to let each cylinder “breath” outside air directly through the carburetor. As a result, air is no longer controlled restricted by the confines of the air box, but is also no longer filtered by the air filter. The same is true for motorcycles employing aftermarket velocity stacks. Velocity stacks are fluted intake ports at each carburetor that employ no filtration, and give an aesthetically pleasing organ pipe appearance. As an alternative to the unfiltered approach, “pod” filters may be provided. Pod filters are typically cylindrical or conical shaped filters and have paper, mesh or foam elements that offer minimal resistance to air flow and will be familiar to one skilled in the art. Although the majority of pod filters are individual pod filters provided at each cylinder inlet or carburetor inlet, some are designed to accommodate either two or four carburetors.
Unfortunately, current direct intake pod filters and velocity stacks suffer from some deficiencies, particularly when used with motorcycle engines. First, without the protection of the air box, the filter is susceptible to tuning issues from ambient conditions such as side winds or rain that alter the filter's ability to pass air to the engine and thus alter the engine's performance. Second, without the air flow control of the air box, too much air can be provided to the engine upsetting the air-fuel mixture balance. It is commonly necessary to replace jets of the carburetor(s) (or “rejet the carbs”) to attempt match the new air flow characteristics of a bike that has had conventional pod type filters installed in place of the OEM air box and filter. Aftermarket velocity stacks must also match the new air flow characteristics of a bike that was designed for an OEM air box. In both cases rejetting is a very complicated and time-consuming procedure which could be avoided with a tunable pod filter/velocity stack that gives control over the airflow provided to the engine.
What is needed is a more convenient tunable pod filter for combustion engines, and particularly motorcycle engines, and a, method for tuning the pod filter that eliminates the need for rejetting the carburetors when replacing stock air box filters with pod filters.